1. Field of the Invention
The present invention relates to an apparatus for monitoring open state of the secondary terminals of a Current Transformer (CT), more specifically speaking, relates to an apparatus that is connected directly to the secondary terminals of the CT and prevents the damage of the CT and the electric shock when the secondary terminals are opened, by making it an input signal and operating the relay circuit and so shorting the secondary terminals of the CT. Moreover the present invention relates to an art that prevents a misjudgment of the open state of the secondary terminals considering the operating time of other relays connected to the secondary terminals of the CT.
2. Description of the Related Art
A Current Transformer (‘CT’hereinafter) is a transformer that is used to expand the measuring ranges of the AC ammeter by gaining small current from large AC current. The CT has primary coil whose number of winding wire is small and secondary coil whose number of winding wire is large and each coil is rolled up at an iron core like a transformer, and a measuring apparatus like an ammeter, a wattmeter, and a relay is connected to the secondary coil. Moreover, the rated current of the primary current of the CT is from several tens of amperes to several thousand amperes, and typically the rated secondary current is almost 5 amperes, with the ratio of primary to secondary current being in inverse proportion to the number of the winding wire of coils.
Meanwhile shorting the secondary terminals of the CT is safe, but opening it is very dangerous. This is because if the secondary coil is opened in the state of flowing current at the primary coil of CT, the primary current magnetizes all iron cores, the iron cores are saturated and generate heat, so there are dangers of damage of the coil, explosion of the CT, and electric shock. Therefore if the inner circuit of measuring apparatus like the ammeter, wattmeter connected to secondary coil of the CT is opened or the secondary coil of the CT is opened for the other reason, a circuit that can short the open secondary terminals at once needs to be connected to the secondary terminals.
A monitoring circuit like the above monitors the open state and shorts the terminals. After that, short state must be maintained continually until the manager finds the cause of opening of the secondary terminals of the CT and eliminate it. If it changes to open state suddenly during the manager's repair, an accident of electric shock may happen.
Regardless of this danger, there are almost no measures to prevent accidental opening of the secondary coil of the CT yet, and there is a need for an invention to prevent such accidental opening and to minimize the associated danger.
In addition, in case of testing or repairing the CT and other measuring apparatus like the ammeter, wattmeter, relay, and recorder connected to the electric equipment, maintaining short state safely during the work is necessary to prevent the electric shock.
In this case since no special apparatus that can short the secondary terminals of the CT has been prepared, there were many inconvenient things. That is, as the secondary terminals of the CT must be shorted in the state of supplying the sources of electricity without stopping the operation of the total electric equipment, danger of electric shock always existed.